The present invention relates to a method of marking ceramic member made of ceramics, a low-temperature fired material and glass, which is used as an insulating substrate of a package for containing a semiconductor device, and a marked ceramic member.
As a package for containing a semiconductor device, which is used for containing a semiconductor device, particularly a semiconductor integrated circuit device, for example, those comprising a package body made of ceramics such as alumina ceramics, low-temperature fired ceramics and electrical insulating materials such as glass, and an external lead terminal for electrically connecting the semiconductor device to an external circuit have been known.
In the package for containing the semiconductor device, a mark is formed occasionally on the external surface of the package in order to enable an operator or an automatic assembling machine to recognize product information such as product number and a direction of the package.
According to a conventionally known marking method, marking is conducted by irradiating the surface of the package body with laser light to solve the surface of the package body.
However, when using laser light, marking conditions drastically vary depending on characteristics such as heat resistance and color tone of a material to be marked such as package body. In case where the surface of the material to be marked shows a white or light color, it was difficult to form a clear contrast of color tone between the marking portion and the non-marking portion. Furthermore, a transparent product had such a drawback that the time required for marking becomes longer because laser light is easily transmitted.
To solve these drawbacks, various suggestions have hitherto been made. For example, Unexamined Patent Publication (Kokai) No. 4-210882 discloses a laser marking method comprising coating the surface of a ceramic member with a coating composition, irradiating the surface with laser light to form a mark, and removing the excessive coating composition. According to this method, since the coating composition is vaporized in a range irradiated with laser light and the surface of the ceramic member is carved, vapor of the coating composition is introduced into the formed concave portion, where the coating composition is solidified and deposited, and then baked to develop a black color.
Examined Patent Publication (Kokoku) No. 7-61551 discloses a laser marking method comprising irradiating a ceramic material or glass containing a radiation-sensitive additive made of an inorganic pigment such as zirconium vanadium yellow with laser light, thereby to induce a change in color in a range irradiated with laser light.
Unexamined Patent Publication (Kokai) No. 1-141091 discloses a laser marking method comprising etching the external surface of ceramics colored black by adding chromium oxide using a corrosive chemical such as hydrofluoric acid, and irradiating the etched surface with laser light to form a mark. According to this method, an original color of ceramics is lightened by the etching treatment, while the color changes to a deeper color within the laser light irradiation range so that a contrast of color between the range irradiated with laser light and the etched surface other than the range is enhanced, thereby making it easy to recognize the marking portion as the range irradiated with laser light.
The method described in Unexamined Patent Publication (Kokai) No. 4-210882 has such a drawback that the production cost becomes larger because of large number of processes such as coating of a coating composition, irradiation with laser light and removal of the coating composition.
The method of Examined Patent Publication (Kokoku) No. 7-61551 has such a drawback that, since a large amount of the additive (radiation-sensitive additive) other than the product composition such as ceramics and glass, an adverse influence is liable to be exerted on characteristics of the product and, therefore, the method can not be applied to only a product having a specific composition. Since control of a frequency of laser light is required to cause color change of the additive, process control becomes complicated.
The method described in Unexamined Patent Publication (Kokai) No. 1-141091 has such a drawback that, since the surface of ceramics is etched by using a corrosive chemical, when a metallized layer is formed on the surface of the ceramics, the strength of bonding between the metallized layer and ceramics is reduced. Since the process of etching is required, the number of processes increases, resulting in high production cost.
Furthermore, a conventional laser marking method has such a problem that, since the low-temperature fired material or glass product containing a large amount of a glass component hardly absorb laser light, the laser light irradiation time becomes larger, resulting in poor productivity.
A main object of the present invention is to provide a method of marking a ceramic member, capable of easily forming a mark having excellent visibility in a short time without increasing the number of processes.
Another object of the present invention is to provide a ceramic member on which a mark having excellent visibility is formed.
The present inventors have intensively studied to attain the objects described above. As a result, they have paid attention to the fact that a compound capable of developing different color tones by heating in different atmospheres exists, and found a new fact that a mark having excellent visibility can be formed easily in a short time without increasing the number of processes by containing the compound as a color changing agent in a ceramic green body, followed by firing in different atmospheres and further heat treatment. Thus, the present invention has been completed.
The marking method of the present invention comprises firing, in an atmosphere, a ceramic green body containing a color changing agent capable of developing different color tones by heating in different atmospheres, and heating a specific portion of the resulting sintered body in the other atmosphere to form a marking portion whose color tone is different from that of the other portion.
The different atmospheres are an oxidizing atmosphere and a reducing atmosphere, and the specific portion of the sintered body obtained by firing in any one of the atmospheres is heated in the other atmosphere.
The specific portion of the sintered body is preferably heated by irradiation with laser light, thereby making it possible to form a mark having excellent visibility in a short time.
The color changing agent includes, for example, a simple substance, an oxide or a composite oxide of at least one metal selected from the group consisting of Mn, Fe, V, Se and Cu. These metal elements or compounds have a property capable of changing the color tone by heating in different atmospheres.
At least 0.05% by weight of the color changing agent is preferably contained in the ceramic green body.
A ceramic member of the present invention has a marking portion, whose color tone is different from that of the other portion, formed on the surface. The ceramic member comprises ceramics containing a color changing agent, and the valence of the color changing agent in the marking portion is different from that of the color changing agent in the portion other than the marking portion.
In this case, the valence of the color changing agent in the marking portion is larger than that in the portion other than the marking portion.
The ceramics include, for example, glass ceramics. A circuit made of copper or silver is formed on the surface or in the ceramic member.
The other objects and advantages of the present invention will becomes apparent from the following detailed description.
In the present invention, the color changing agent capable of developing different color tones by heating in different atmospheres refers to the above-described compound capable of changing a color tone by a heat treatment in an oxidizing atmosphere and a heat treatment in a reducing atmosphere, and specific examples include a simple substance, an oxide or a composite oxide of metals such as Mn, Fe, V, Se and Cu. The color developing agent is preferably used in the form of the oxide. For example, a color is hardly developed even if MnO2 is added in the ceramic composition, followed by heat treatment in the reducing atmosphere, but a violet color is developed when subjecting to a heat treatment in the oxidizing atmosphere.
Such a change in color is caused by oxidizing MnO2 to change the valance of Mn to 6 or 7 from 4.
Examples of change in color tone of the other color changing agents are described below.
The oxidizing atmosphere refers to a heat treatment in an air or an oxygen atmosphere. The reducing atmosphere refers to a heat treatment in a nitrogen atmosphere or a hydrogen atmosphere.
The ceramic green body may be heat-treated in an oxidizing or reducing atmosphere after firing in a high-vacuum atmosphere. In this case, the color changing agent does not develop or change a color by the heat treatment in the high-vacuum atmosphere, but can develop or change into a specific color by the heat treatment in the oxidizing or reducing atmosphere.
The color changing agent is preferably contained in the ceramic green body in the amount of at least 0.05% by weight. When the amount of the color changing agent is less than 0.05% by weight, there is a fear that a mark can not be identified even if the color is changed. The upper limit of the amount of the color changing agent is not specifically limited as far as it does not exert an adverse influence on characteristics of ceramics, but the amount is preferably 5% by weight or less. The color changing agents may be used in combination.
For the purpose of uniformly coloring ceramics, a coloring agent can be contained in the ceramic green body, together with the color changing agent. The coloring agent includes, for example, Cr2O3 (green), Co2O3 (Prussian blue) and Er2O3 (pink) (color in the parenthesis represents a color developed by each coloring agent). When using the coloring agent, the amount of the coloring agent contained in the ceramic green body is preferably 5% by weight or less.
The ceramic green body containing the color changing agent is obtained by mixing various raw powders such as glass ceramic and alumina powders with a predetermined amount of the color changing agent, adding a small amount of a synthetic resin binder to the mixed powders, and forming the resulting admixture using a known forming means. The forming means includes, for example, doctor blade method, press forming method, rolling method and calender rolling method.
After the completion of forming, the resulting ceramic green body is fired. On firing, the green body is heated to the temperature of about 700xc2x0 C. to remove the binder component incorporated for forming, and then properly fired. The firing is conducted at the temperature of about 800 to 1050xc2x0 C. in case of glass ceramics, while it is conducted at the temperature of 1300 to 1700xc2x0 C. in case of alumina. On firing, the coloring agent incorporated in the green body develops a color.
After the completion of firing, the resulting sintered body is marked by irradiating the specific portion with laser light. The laser light used for irradiation is preferably laser light capable of heating the surface of the sintered body to at least 750xc2x0 C. and, for example, YAG laser and ruby laser can be used.
In this case, since the color changing agent in the present invention can rapidly change the color by a heat treatment in different atmospheres, a laser irradiation time can be remarkably reduced as compared with a conventional laser marking method and the marking can be usually conducted at an irradiation rate of about 10 to 20 mm/second. Accordingly, the productivity is improved and the surface layer of the sintered body is hardly damaged by irradiation with laser light.
The ceramic member to which the method of the present invention is applied includes, for example, ceramics such as alumina, mullite and aluminum nitride; SiO2xe2x80x94Al2O3xe2x80x94CaOxe2x80x94, SiO2xe2x80x94Al2O3xe2x80x94B2O3xe2x80x94 and SiO2xe2x80x94BaOxe2x80x94B2O3xe2x80x94Al2O3xe2x80x94CaO-based glasses; and low-temperature fired materials (so-called glass ceramics) prepared by adding 5 to 80% by volume of fillers such as alumina, quartz, enstatite, mullite and forsterite in these glasses.
It has hitherto been very difficult to form a mark to the low-temperature fired material and glass, because they contain a glass component. However, a mark having excellent visibility can be formed easily by irradiation with laser light in a very short time according to the method of the present invention, which is particularly useful.
The marking method of the present invention is particularly suited to form a mark on an insulating substrate in a package for containing a semiconductor device, and to form a mark of various product informations and various displays on various electronic parts using a ceramic member, circuit boards wherein a wiring circuit layer is formed on the surface of or in an insulating substrate, various structural ceramic parts, and ceramic processed parts.
The marking method of the present invention is most useful to a package or circuit board wherein a circuit made of silver or copper, formed by firing together with an insulating substrate, was formed on the surface of or in the insulating substrate made of the low-temperature firing material.